Magnetorheological compositions generally include a mixture of magnetic particles and a carrier medium. When a magnetorheological composition is subjected to a magnetic field, the viscosity of the magnetorheological composition generally increases substantially so that the magnetorheological composition may behave as a solid rather than a fluid. That is, when not subjected to the magnetic field, i.e., when “off-state”, the magnetic particles may be distributed substantially homogeneously in the carrier medium. In contrast, when subjected to the magnetic field, i.e., when “on-state”, the magnetic particles may align in chain-like structures disposed parallel to the magnetic field and perpendicular to the direction of flow. Therefore, flow may be impeded so that the magnetorheological composition behaves as a solid. Because of such magnetic and rheological properties, magnetorheological compositions may be useful for applications requiring energy absorption.
On-state yield stress at magnetic saturation, i.e., a value beyond which the magnetorheological composition begins to flow, may be increased by increasing a magnetic particle concentration in the magnetorheological composition. However, increased magnetic particle concentration generally increases the weight, and therefore the density and cost, of the magnetorheological composition.
Additionally, on-state yield stress at magnetic saturation may also be increased by increasing a saturation magnetization of the magnetic particles. However, magnetic particles having increased saturation magnetization are often unavailable in commercial quantities, thereby further increasing the cost of the magnetorheological composition.